The Staphylococcal Pore-forming Leukotoxins Open Ca 2+ Channels in the Membrane of Human Polymorphonuclear Neutrophils

Abstract

The ability of leukotoxins secreted by Staphylococcus aureus to modify the permeability of the membrane of human polymorphonuclear neutrophils has been studied by spectrofluorometry and appropriate fluorescent probes. This family of bicomponent leukotoxins is constituted by, at least, three pairs of proteins: LukS-PV/LukF-PV, HlgA/HlgB, HlgC/HlgB. After binding of both components to the membrane, each pair induces influxes of divalent cations and ethidium in polymorphonuclear neutrophils, although with different intensities. The influx of divalent cations appears sooner than the influx of ethidium. The pathway for divalent cations is not permeable to monovalent cations (Na+, K+, ethidium+) and is blocked by Ca2+ channel inhibitors that do not block the fluxes of ethidium and monovalent cations. It is concluded that the leukotoxins bind to a receptor linked to a divalent cation-selective channel or to the channel itself which is activated. Then, the leukotoxins open a second pathway by insertion into the membrane and subsequent formation of aspecific pores allowing an influx of ethidium.

Enhancement of bacterial virulence by antibody neutralization of immune-activating toxins

“…Our results went beyond questioning the value of anti-staphylococcal antibodies in prevention of infections by S. aureus (as some studies have found that high titers of antibodies to S. aureus are not effective in preventing re-infection [16][17][18][19][20] ), but supported the hypothesis that the manner by which PVL plays a role in CA-MRSA pathogenesis is by antibody-mediated neutralization of the host's innate response activated by sub-lytic amounts of PVL produced early in the course of infection. Mechanistically, we confirmed that sub-lytic concentrations of PVL induced the opening of calcium ion channels in PMNs, 21,22 a hallmark of PMN activation, 23 and showed that antibodies directed to PVL inhibited this activation (Fig. 2B).…”

Heavy chain-only antibodies and tetravalent bispecific antibody neutralizing Staphylococcus aureus leukotoxins

“…Human PMNs are activated by very low concentration of leukotoxins, and, thus, activation is difficult to avoid. Calcium entry in hPMNs relies on leukotoxins compounds binding and oligomerization (33). We measured variation of intracellular calcium concentrations in hPMNs by flow cytometry.…”

The Bicomponent Pore-Forming Leucocidins of Staphylococcus aureus

“…In this work, it was proposed that ethidium entry into host cells, but not calcium entry, is a definitive marker of pore formation by leucocidins (152,153). In contrast, calcium entry upon leucocidin treatment is believed to occur prior to pore formation and is mediated by the opening of membrane divalent cation channels (154,155). In the 10 years following this early assessment of the leucocidin pore, a number of studies using gamma-hemolysin and PVL served to dramatically increase our understanding of the molecular characteristics of pore formation.…”